Porous lithium fluoride as well as preparation method, device and application thereof

Abstract

The invention provides porous lithium fluoride as well as a preparation method, device and application thereof, and the preparation method of the porous lithium fluoride comprises the following steps: 1) carrying out heat treatment on a mixed system to obtain a reaction solution; wherein the mixed system comprises lithium fluoride and a hydrofluoric acid solution, during heat treatment, the Reynolds number of the mixed system is larger than 5000, the temperature is 30-60 DEG C, and the time is 0.2-5 min; (2) the reaction liquid is subjected to atomization treatment, an atomization system is obtained, and the particle size of liquid drops formed in the atomization system ranges from 30 micrometers to 200 micrometers; and 3) under the pressure of 0.1-0.5 MPa, performing thermal shrinkage treatment on the atomization system for 1-20 minutes by using inert gas with the temperature not lower than 200 DEG C to obtain the porous lithium fluoride. According to the preparation method of the porous lithium fluoride, the porous lithium fluoride with high specific surface area, high porosity and proper particle size can be prepared, and the preparation method is simple in process and high in production efficiency.

Description

Technical Field

[0001] The present invention relates to porous lithium fluoride, in particular to porous lithium fluoride and a preparation method, device and application thereof, belonging to the technical field of chemical material preparation. Background Art

[0002] With the rapid development of the new energy industry, especially the lithium battery market, the demand for lithium hexafluorophosphate, as a key component of electrolyte lithium salt, is growing. At present, the industry usually mixes lithium fluoride powder with an excess of hydrofluoric acid solution, and then under specific thermodynamic conditions, phosphorus pentafluoride gas is caused to dissolve in the hydrofluoric acid solution and react with lithium fluoride to synthesize lithium hexafluorophosphate.

[0003] The traditional production process of lithium hexafluorophosphate usually relies on intermittent kettle reaction or tower reaction equipment, which has the problems of limited solid-liquid interface contact area and low mass transfer efficiency, which limits the degree of reaction between phosphorus pentafluoride gas and lithium fluoride particles, and is prone to local inadequate reaction and low conversion rate. In addition, the extremely high concentration of hydrofluoric acid remaining after the reaction and the unreacted lithium fluoride solid matter together lead to serious equipment corrosion problems, which also greatly increases the difficulty of effectively crystallizing pure lithium hexafluorophosphate from a complex solution rich in hydrofluoric acid and solid suspensions, thereby causing product quality fluctuations and yield declines.

[0004] Therefore, those skilled in the art are in urgent need of developing a porous lithium fluoride to improve the product quality and production efficiency of lithium hexafluorophosphate. Summary of the invention

[0005] The present invention provides a method for preparing porous lithium fluoride. The method can prepare porous lithium fluoride with high specific surface area, high porosity and suitable particle size, and the method has simple process and high production efficiency.

[0006] The present invention provides a porous lithium fluoride having a high specific surface area, a high porosity and a suitable particle size. The porous lithium fluoride is used as a raw material in the preparation of lithium hexafluorophosphate, which can improve the product quality and production efficiency of the lithium hexafluorophosphate.

[0007] The present invention provides a porous lithium fluoride device, which can provide excellent preparation conditions for the preparation of porous lithium fluoride and is conducive to the preparation of porous lithium fluoride with high specific surface area, high porosity and suitable particle size.

[0008] The invention provides a method for preparing lithium hexafluorophosphate. The method can prepare lithium hexafluorophosphate with high product quality, and the method has simple process and high production efficiency.

[0009] The present invention also provides an electrolyte, which is prepared by using porous lithium fluoride as a lithium salt, has high lithium conductivity, and can make the battery present excellent electrochemical performance.

[0010] The present invention provides a method for preparing the porous lithium fluoride as described above, which comprises the following steps:

[0011] 1) heat-treating a mixed system including lithium fluoride and a hydrofluoric acid solution to obtain a reaction solution;

[0012] During the heat treatment, the Reynolds number of the mixed system is greater than 5000, the temperature is 30-60° C., and the time is 0.2-5 min;

[0013] 2) atomizing the reaction solution to obtain an atomization system with a droplet size of 30-200 μm;

[0014] 3) The atomization system is subjected to a heat shrinkage treatment for 1-20 min using an inert gas at a temperature not lower than 200° C. at 0.1-0.5 MPa to obtain the porous lithium fluoride.

[0015] The method for preparing porous lithium fluoride as described above, wherein the mixed system is prepared by a method comprising the following process:

[0016] Premixing the lithium fluoride with a hydrofluoric acid solution at 20-40° C. and 0.3-3 MPa to obtain the mixed system;

[0017] Wherein, the reaction time of the premixing treatment is 1-3 minutes.

[0018] The method for preparing porous lithium fluoride as described above, wherein the purity of the lithium fluoride is 99-99.5%, D50 is 20-100 μm, and the specific surface area is 200-700 m 2 / g.

[0019] In the method for preparing porous lithium fluoride as described above, the mass percentage of the hydrofluoric acid solution is 95-99%.

[0020] The method for preparing porous lithium fluoride as described above, wherein the step 3) further comprises the following steps:

[0021] The mixed gas obtained after the heat shrinkage treatment is condensed to obtain recovered hydrofluoric acid and recovered inert gas, and then the recovered hydrofluoric acid is returned to the pre-mixing treatment, and the recovered inert gas is returned to the heat shrinkage treatment.

[0022] The present invention provides a porous lithium fluoride, wherein the specific surface area of ​​the porous lithium fluoride is 600-1400m 2 / g, porosity 30-80%;

[0023] The D50 of the porous lithium fluoride is 20-100 μm.

[0024] The porous lithium fluoride as described above, wherein the purity of the porous lithium fluoride is 99-99.5%, and the mass percentage of hydrogen fluoride in the porous lithium fluoride is less than 500 ppm.

[0025] The present invention also provides a porous lithium fluoride device, which includes a heat treatment unit, an atomization unit and a heat shrinkage treatment unit;

[0026] Wherein, the reaction liquid outlet of the heat treatment unit is connected to the inlet of the atomization unit;

[0027] The atomizing unit is used for the atomizing treatment, and the heat shrinking treatment unit is used for the heat shrinking treatment.

[0028] The porous lithium fluoride device as described above, wherein the device further comprises a pre-mixing unit, and the outlet of the pre-mixing unit is connected to the inlet of the heat treatment unit.

[0029] The porous lithium fluoride device as described above, wherein:

[0030] The device also includes a condensation unit, which is used for condensation treatment of the mixed gas, wherein the liquid phase outlet of the condensation unit is connected to the inlet of the premixing unit, and the gas phase outlet of the condensation unit is connected to the gas phase inlet of the heat shrinkage treatment unit.

[0031] The present invention also provides a method for preparing lithium hexafluorophosphate, wherein the lithium hexafluorophosphate is prepared by using the porous lithium fluoride as a raw material.

[0032] The present invention also provides an electrolyte, wherein the electrolyte comprises lithium hexafluorophosphate prepared by using the porous lithium fluoride as a raw material.

[0033] The preparation method of porous lithium fluoride of the present invention prepares porous lithium fluoride by a three-step method, which can effectively promote mass transfer and mixing between lithium fluoride and hydrofluoric acid solution, realize continuous reaction of lithium fluoride and hydrofluoric acid to generate lithium hydrogen fluoride, and can effectively increase the mass transfer interface area of ​​lithium hydrogen fluoride, which is conducive to rapid thermal decomposition and volume shrinkage of lithium hydrogen fluoride, so that the specific surface area, porosity and D50 of porous lithium fluoride reach the above range. In addition, the preparation method has a simple process, is easy to operate, and can realize continuous production of porous lithium fluoride, which is conducive to improving the production efficiency of porous lithium fluoride.

[0034] The porous lithium fluoride provided by the present invention has a high specific surface area, a high porosity and a suitable particle size, can make phosphorus pentafluoride gas diffuse rapidly on its surface and in the internal microporous structure, and can make lithium fluoride better dissolved in the hydrogen fluoride solution, thereby improving the dissolution contact efficiency and reaction rate of phosphorus pentafluoride gas and lithium fluoride, effectively reducing the residual unreacted lithium fluoride, and facilitating the output of high-quality lithium hexafluorophosphate and the improvement of raw material conversion rate, and can reduce the amount of hydrogen fluoride used in the preparation process of hexafluorophosphate, simplify the later processing steps, and also can reduce the influence on equipment corrosion, improve energy utilization, and comply with environmental protection requirements.

[0035] The present invention also provides a porous lithium fluoride device, which can provide preparation conditions for the preparation of porous lithium fluoride, thereby realizing the preparation of porous lithium fluoride with high specific surface area, high porosity and suitable particle size.

[0036] The present invention also provides a method for preparing lithium hexafluorophosphate. The method adopts the above-mentioned porous lithium fluoride and phosphorus pentafluoride to react in a hydrofluoric acid solution, which can increase the contact area between phosphorus pentafluoride and porous lithium fluoride and improve the reaction efficiency, thereby realizing the preparation of high-purity lithium hexafluorophosphate, and has high production efficiency and high raw material conversion rate.

[0037] The present invention also provides an electrolyte, which includes lithium hexafluorophosphate prepared by using the porous lithium fluoride as a raw material, and can make the electrolyte have high lithium conductivity, so that the battery exhibits excellent electrochemical performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 The present invention provides a flow chart of the device. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] The present invention provides a method for preparing porous lithium fluoride, comprising the following steps:

[0041] 1) heat-treating a mixed system including lithium fluoride and a hydrofluoric acid solution to obtain a reaction solution;

[0042] During the heat treatment, the Reynolds number of the mixed system is greater than 5000, the temperature is 30-60°C, and the time is 0.2-5min;

[0043] 2) atomizing the reaction liquid to obtain an atomization system with a droplet size of 30 to 200 μm;

[0044] 3) Under a pressure of 0.1-0.5 MPa, the atomization system is subjected to a heat shrinkage treatment for 1-20 min using an inert gas at a temperature not lower than 200° C. to obtain porous lithium fluoride.

[0045] Specifically, step 1) in a tubular reactor including a small diameter pipe and equipped with SK, SX or other composite internal components, the flow rate, flow velocity of the mixed system and the diameter of the tubular reactor are controlled to ensure that the Reynolds number of the mixed system composed of lithium fluoride and hydrofluoric acid solution is greater than 5000, the temperature is controlled within the range of 30-60° C., and heat treatment is performed for 0.2-5 min to obtain a reaction solution.

[0046] The present invention does not limit the ratio of lithium fluoride to hydrofluoric acid solution in the mixed system, and the ratio can be selected according to actual needs.

[0047] The present invention does not limit the parameters of the purity and specific surface area of ​​lithium fluoride, and they can be selected according to actual needs.

[0048] The present invention does not limit the concentration of the hydrofluoric acid solution, and it can be selected according to actual needs.

[0049] The present invention can effectively promote mass transfer and mixing between lithium fluoride and hydrofluoric acid solution by controlling the Reynolds number of the mixed system, and then heat-treating the mixed system to enable continuous reaction of lithium fluoride and hydrofluoric acid to generate lithium hydrogen fluoride.

[0050] Step 2), the reaction solution obtained in step 1) is dispersed into small droplets through a nozzle or a high-speed airflow to obtain an atomization system, wherein the particle size of the droplets in the atomization system is 30-200 μm.

[0051] The present invention does not limit the specific parameters of the atomization treatment, and can be selected according to actual needs, as long as the particle size of the droplets in the atomization system reaches 30-200 μm. When the particle size of the droplets is within this range, the mass transfer interface area of ​​lithium fluoride is large enough, which is conducive to the subsequent endothermic decomposition of the lithium fluoride droplets to generate porous lithium fluoride. If the particle size of the droplets is less than 30 μm, the equipment requirements for the atomization treatment are high, the atomization cost is high, and the particle size of the prepared porous lithium fluoride is too small, which is not conducive to subsequent applications; if the particle size of the droplets is greater than 200 μm, it is difficult for the lithium fluoride droplets to absorb enough heat to remove the solvent and dry, making it difficult to perform heat shrinkage treatment, resulting in the porous lithium fluoride having a large particle size and a high hydrogen fluoride content.

[0052] Step 3), under a pressure of 0.1-0.5 MPa, use an inert gas to purge the droplets in the atomization system, the temperature of the inert gas is not less than 200° C., and the heat shrinkage treatment time is 1-20 min to obtain porous lithium fluoride.

[0053] The present invention does not limit the selection of the inert gas, for example, nitrogen, helium, etc. may be used.

[0054] The invention uses hot inert gas to purge lithium hydrogen fluoride gas under a certain pressure environment, so that lithium hydrogen fluoride can quickly absorb heat, thereby quickly removing the solvent and drying it, and decomposing it into lithium fluoride and hydrogen fluoride. As the hydrogen fluoride is removed by the inert gas, the lithium fluoride shrinks in volume to obtain porous lithium fluoride.

[0055] The invention prepares porous lithium fluoride by a three-step method. Firstly, a mixed system including lithium fluoride and hydrofluoric acid solution is subjected to heat treatment, which can effectively promote mass transfer and mixing between lithium fluoride and hydrofluoric acid solution, and realize continuous reaction of lithium fluoride and hydrofluoric acid to generate lithium hydrogen fluoride. Then, the reaction liquid is atomized into small droplets, which can effectively increase the mass transfer interface area of ​​lithium hydrogen fluoride and is beneficial to the subsequent thermal decomposition of lithium hydrogen fluoride. Then, the lithium hydrogen fluoride droplets are subjected to thermal shrinkage treatment, so that the lithium hydrogen fluoride is rapidly thermally decomposed and volume-shrunk, thereby making the specific surface area of ​​the porous lithium fluoride reach 600-1400m 2 / g, porosity reaches 30-80%, and D50 reaches the range of 20-100 μm. In addition, the preparation method of porous lithium fluoride of the present invention is simple in process and easy to operate, and can realize continuous production of porous lithium fluoride, which is conducive to improving the production efficiency of porous lithium fluoride.

[0056] In a specific embodiment, the mixed system is prepared by a method comprising the following process: premixing lithium fluoride and hydrofluoric acid solution at 20-40° C. and 0.3-3 MPa to obtain a mixed system; wherein the reaction time of the premixing treatment is 1-3 min.

[0057] The present invention does not limit the specific method of premixing the lithium fluoride and the hydrofluoric acid solution, which can be selected according to actual needs. For example, the lithium fluoride and the hydrofluoric acid solution can be stirred or homogenized.

[0058] The present invention prepares a mixed system through the above-mentioned premixing treatment, and can mix the hydrogen fluoride solution and the lithium fluoride at a low temperature, thereby avoiding local overheating when the lithium fluoride and the hydrogen fluoride solution are mixed to cause safety hazards, and can ensure uniform mixing of the lithium fluoride and the hydrofluoric acid solution, which is beneficial to the subsequent heat treatment, and avoids the stratification of the lithium fluoride and the hydrofluoric acid solution during the heat treatment, resulting in low production efficiency of the lithium hydrogen fluoride, thereby improving the production efficiency of the porous lithium fluoride, and can improve production safety.

[0059] In a specific embodiment, the purity of lithium fluoride is 99-99.5%, for example, the purity is 99%, 99.1%, 99.2%, 99.3%, 99.4% or 99.5%, etc., D50 is 20-100 μm, for example, D50 is 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm or 100 μm, etc., and the specific surface area is 200-700 m 2 / g, for example, the specific surface area is 200m 2 / g、300m 2 / g, 400m 2 / g、500m 2 / g、600m 2 / g or 700m 2 When the purity, D50 and specific surface area of ​​lithium fluoride are respectively within the above ranges, it is beneficial for lithium fluoride to react with hydrofluoric acid solution to generate lithium hydrogen fluoride, thereby achieving porous lithium fluoride with high specific surface area, high porosity and appropriate D50, which is beneficial to the subsequent application of lithium fluoride.

[0060] In a specific embodiment, the mass percentage of the hydrofluoric acid solution is 95-99%, for example, 95%, 96%, 97%, 98% or 99%, etc. When the mass percentage of the hydrofluoric acid solution is within the above range, the hydrofluoric acid solution can be evenly mixed with lithium fluoride to generate lithium hydrogen fluoride, thereby achieving successful preparation of porous lithium fluoride, and avoiding excessively high hydrogen fluoride content in porous lithium fluoride due to excessively high concentration of the hydrofluoric acid solution, thereby improving the purity of porous lithium fluoride, and saving raw material costs, which is conducive to large-scale production of porous lithium fluoride. At the same time, it can avoid that the concentration of the hydrofluoric acid solution is too low, resulting in the inability of lithium fluoride and the hydrofluoric acid solution to form a relatively stable lithium hydrogen fluoride, resulting in the subsequent decomposition of lithium hydrogen fluoride too early, and the shrinkage treatment of lithium fluoride is not achieved, resulting in a small specific surface area of ​​porous lithium fluoride, which is not conducive to the subsequent application of porous lithium fluoride.

[0061] In a specific embodiment, step 3) further includes the following steps: condensing the mixed gas obtained after the heat shrinkage treatment to obtain recovered hydrofluoric acid and recovered inert gas, and then returning the recovered hydrofluoric acid to the pre-mixing treatment, and returning the recovered inert gas to the heat shrinkage treatment.

[0062] After the present invention performs heat shrinkage treatment on the atomization system, lithium bifluoride is thermally decomposed and volume shrinks to obtain hydrofluoric acid gas and porous lithium fluoride, and the hydrofluoric acid gas is mixed with an inert gas to form a mixed gas. The present invention performs condensation treatment on the mixed gas, and after the condensation treatment, the hydrofluoric acid gas is condensed into hydrofluoric acid liquid, which is returned to the premixing treatment and used as a raw material to react with lithium fluoride to obtain lithium bifluoride; and after the condensation treatment, the inert gas is still in a gas phase state, and its temperature is high, so it is returned to the heat shrinkage treatment and used as a heat source again to perform thermal decomposition and volume shrinkage on the lithium bifluoride. The present invention does not limit the specific parameters of the condensation treatment.

[0063] The present invention can recover the heat of the inert gas by condensing the mixed gas, and can circulate the hydrofluoric acid and the inert gas, thereby saving energy and reducing consumption, and helping to reduce the production cost of porous lithium fluoride.

[0064] The present invention provides a porous lithium fluoride having a specific surface area of ​​600-1400 m 2 / g, for example, the specific surface area is 600m 2 / g, 650m 2 / g、700m 2 / g, 750m 2 / g、800m 2 / g, 850m 2 / g、900m 2 / g, 950m 2 / g、1000m 2 / g, 1050m 2 / g、1100m 2 / g, 1150m 2 / g、1200m 2 / g, 1250m 2 / g、1300m 2 / g, 1350m 2 / g or 1400m 2 / g, etc., and the porosity is 30-80%, for example, the porosity is 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75% or 80%, etc.; the D50 of the porous lithium fluoride is 20-100μm, for example, D50 is 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm, 65μm, 70μm, 75μm, 80μm, 85μm, 90μm, 95μm, 100μm, etc.

[0065] The porous lithium fluoride of the present invention has a high specific surface area, a high porosity and a suitable particle size. The porous lithium fluoride is used as a raw material in the preparation of lithium hexafluorophosphate, which is beneficial to improving the product quality and production efficiency of lithium hexafluorophosphate. The inventor analyzed the reason and believed that the reason may be that when the specific surface area, porosity and particle size of porous lithium fluoride are respectively within the above ranges, on the one hand, the diffusion capacity of phosphorus pentafluoride gas on the surface of porous lithium fluoride and in the internal microporous structure is greatly enhanced, thereby improving the dissolution contact efficiency and reaction rate of phosphorus pentafluoride gas and lithium fluoride, effectively reducing the residual unreacted lithium fluoride, and contributing to the output of high-quality lithium hexafluorophosphate and the improvement of raw material conversion rate. It can not only reduce the amount of hydrogen fluoride used in the preparation process of hexafluorophosphoric acid and simplify the post-processing process, but also be easy to control due to the higher crystal concentration, and at the same time, it can also reduce the impact on equipment corrosion, improve energy utilization, and comply with environmental protection requirements; on the other hand, when porous lithium fluoride is in contact with hydrogen fluoride solution, porous lithium fluoride with a high specific surface area can be infiltrated by hydrogen fluoride solution faster, so that porous lithium fluoride can be better dissolved, thereby increasing the concentration of porous lithium fluoride in hydrogen fluoride solution, and then can improve the reaction efficiency of phosphorus pentafluoride gas and porous lithium fluoride, and improve the raw material conversion rate.

[0066] Specifically, the specific surface area of ​​the porous lithium fluoride of the present invention can be obtained by BET test, the porosity can be obtained by pycnometer test, and D50 can be obtained by laser particle size analyzer test.

[0067] In a specific embodiment, the purity of the porous lithium fluoride is 99-99.5%, for example, the purity is 99%, 99.05%, 99.1%, 99.15%, 99.2%, 99.25%, 99.3%, 99.35%, 99.4%, 99.45%, 99.5%, etc., and the mass percentage of hydrogen fluoride in the porous lithium fluoride is less than 500ppm. The high purity of the porous lithium fluoride is conducive to improving the purity of the prepared lithium hexafluorophosphate, and in the subsequent battery application, it can reduce the probability of battery performance degradation caused by the side reaction of hydrogen fluoride in the battery.

[0068] Specifically, the purity of the porous lithium fluoride and the mass percentage of hydrogen fluoride of the present invention can be obtained by chemical titration testing.

[0069] The present invention also provides a porous lithium fluoride device, such as Figure 1 As shown, the device includes a heat treatment unit, an atomization unit and a heat shrinkage treatment unit; wherein the atomization unit is used for atomization treatment, and the heat shrinkage treatment unit is used for heat shrinkage treatment.

[0070] The heat treatment unit of the present invention is used for continuous reaction of lithium fluoride and hydrofluoric acid solution to generate lithium hydrogen fluoride solution;

[0071] The atomizing unit is used to atomize the lithium hydrofluoride solution into lithium hydrofluoride droplets. For example, the lithium hydrofluoride solution can be atomized into small droplets of 30-200 μm by a high-pressure nozzle.

[0072] The heat shrinkage treatment unit is used to thermally decompose and shrink the volume of lithium fluoride droplets. For example, during the atomization treatment, high-temperature nitrogen gas with a temperature not lower than 200°C can be used as a carrier gas for purging at a pressure of 0.1-0.5MPa, so that the droplets can be quickly desolventized and dried within 0.1-20min, and finally a specific surface area of ​​600-1400m 2 / g, porous lithium fluoride with a porosity of 30-80% and a D50 of 20-100 μm;

[0073] Among them, the reaction liquid outlet of the heat treatment unit is connected with the inlet of the atomization unit, that is, the reaction liquid generated in the heat treatment unit is discharged from the reaction liquid outlet and introduced into the inlet of the atomization unit for atomized material; the outlet of the atomization unit is used to output the atomization system; the gas outlet of the heat shrinkage treatment unit is used to output the mixed gas, that is, the atomization system including lithium hydrogen fluoride droplets generated by the atomization unit is discharged from the atomization system outlet and enters the heat shrinkage treatment unit. After the heat shrinkage treatment, hydrogen fluoride gas and porous lithium fluoride are generated, and the hydrogen fluoride gas is mixed with the inert gas to form a mixed gas.

[0074] In a specific embodiment, Figure 1 As shown, the porous lithium fluoride device also includes a premixing unit, and the outlet of the premixing unit is connected to the inlet of the heat treatment unit. The premixing unit is used for premixing lithium fluoride and hydrofluoric acid solution, and the outlet of the premixing unit is connected to the inlet of the heat treatment unit, that is, the premixed lithium fluoride and hydrofluoric acid solution are led out from the outlet of the premixing unit and introduced through the inlet of the heat treatment unit. The device of the present invention can provide excellent preparation conditions for the preparation of porous lithium fluoride, which is conducive to the preparation of porous lithium fluoride with high specific surface area, high porosity and suitable particle size.

[0075] In a specific embodiment, the device of the present invention further includes a condensation unit, which is used for condensation treatment of the mixed gas, the liquid phase outlet of the condensation unit is connected to the inlet of the premixing unit, and the gas phase outlet of the condensation unit is connected to the gas phase inlet of the heat shrinking treatment unit. The condensing unit can condense the hydrofluoric acid gas in the mixed gas into hydrofluoric acid liquid, and return the hydrofluoric acid liquid to the premixing unit to continue to participate in the preparation of porous lithium fluoride as a raw material, while the remaining inert gas is returned to the heat shrinking treatment unit, and the high temperature of the inert gas is used to decompose and shrink the volume of lithium hydrogen fluoride to achieve the preparation of porous lithium fluoride. The device of the present invention can provide excellent preparation conditions for the preparation of porous lithium fluoride, and can make full use of hydrogen fluoride and inert gases to achieve the purpose of reducing costs and saving energy consumption.

[0076] The present invention also provides a method for preparing lithium hexafluorophosphate. The method adopts the porous lithium fluoride as a raw material to prepare lithium hexafluorophosphate.

[0077] Specifically, the porous lithium fluoride can be mixed with a hydrofluoric acid solution to obtain a mixed system, and then the mixed system is reacted with phosphorus pentafluoride to obtain lithium hexafluorophosphate. The present invention does not limit the concentration of the hydrofluoric acid solution and the purity of the phosphorus pentafluoride, which can be selected according to actual needs. For example, the concentration of the hydrofluoric acid solution can be selected to be 30-47%, and the purity of the phosphorus pentafluoride can be selected to be not less than 99.5%.

[0078] The hydrofluoric acid solution is used as a reaction medium to enable phosphorus pentafluoride gas to dissolve in the hydrofluoric acid solution and fully react with porous lithium fluoride to generate lithium hexafluorophosphate. The present invention uses the high-purity porous lithium fluoride of the present invention to react with phosphorus pentafluoride to prepare lithium hexafluorophosphate. The high specific surface area and high porosity of the porous lithium fluoride can increase the contact area between phosphorus pentafluoride and porous lithium fluoride, promote phosphorus pentafluoride molecules to penetrate into the interior of the porous lithium fluoride, accelerate the consumption of undissolved lithium fluoride, and help improve the reaction efficiency of porous lithium fluoride and phosphorus pentafluoride, so that the production efficiency of lithium hexafluorophosphate is high, the raw material conversion rate is high, and the impurity content in the porous lithium fluoride is low, thereby realizing the preparation of high-purity lithium hexafluorophosphate.

[0079] The present invention also provides an electrolyte, which includes lithium hexafluorophosphate prepared by using the porous lithium fluoride as a raw material. The present invention also provides an electrolyte using lithium hexafluorophosphate prepared by using the porous lithium fluoride as a raw material as a lithium salt. The present invention does not limit the selection of organic solvents in the electrolyte and whether to add additives, which can be selected according to actual needs. The porous lithium fluoride has a high specific surface area and high porosity, can be quickly dissolved in an organic solvent, and an electrolyte with high lithium conductivity is prepared. The porous lithium fluoride has a high purity, which can avoid the side reactions caused by impurities that lead to a decrease in battery performance, thereby allowing the battery to exhibit excellent electrochemical properties.

[0080] Hereinafter, the present invention will be further described in detail through specific examples.

[0081] Example 1

[0082] The preparation process of lithium fluoride provided in this embodiment comprises the following steps:

[0083] 1. At 30° C. and 1 MPa, lithium fluoride and hydrofluoric acid solution are premixed in a premixing unit, the reaction time of the premixing treatment is 2.5 min, to obtain a mixed system, and then the mixed system is heat-treated in a heat treatment unit to obtain a reaction solution;

[0084] Among them, the purity of lithium fluoride is 99.5%, D50 is 75μm, and the specific surface area is 650m 2 / g; the mass percentage of hydrofluoric acid solution is 98.5%;

[0085] The Reynolds number of the mixed system was 6000, the temperature was 45 °C, and the time was 4 min;

[0086] 2. In the atomization unit, the reaction liquid is atomized to obtain an atomization system. The aerosol tester test shows that the droplet size in the atomization system is 120 μm.

[0087] 3. At 0.3 MPa, in a heat shrink unit, the atomization system was heat-shrinked using nitrogen at a temperature of 300° C. for 10 min to obtain porous lithium fluoride.

[0088] The preparation processes of lithium fluoride provided in Examples 1-32 and Comparative Examples 1-6 are substantially the same as those in Example 1, and the specific parameters are shown in Table 1.

[0089] Comparative Example 7

[0090] The preparation process of lithium fluoride provided in this comparative example comprises the following steps:

[0091] 1. At 30° C. and 1 MPa, lithium fluoride and hydrofluoric acid solution are premixed in a premixing unit, the reaction time of the premixing treatment is 2.5 min, to obtain a mixed system, and then the mixed system is heat-treated in a heat treatment unit to obtain a reaction solution;

[0092] Among them, the purity of lithium fluoride is 99.5%, D50 is 75μm, and the specific surface area is 650m 2 / g; the mass percentage of hydrofluoric acid solution is 98.5%;

[0093] The Reynolds number of the mixed system was 6000, the temperature was 45 °C, and the time was 4 min;

[0094] 2. At 0.3 MPa, in a heat shrink unit, the reaction liquid was heat-shrunk using nitrogen at a temperature of 300° C. for 10 min to obtain porous lithium fluoride.

[0095] Comparative Example 8

[0096] The preparation process of lithium fluoride provided in this comparative example comprises the following steps:

[0097] 1. At 30°C and 1MPa, lithium fluoride and hydrofluoric acid solution are premixed in a premixing unit, and the reaction time of the premixing treatment is 2.5min to obtain a mixed system;

[0098] Among them, the purity of lithium fluoride is 99.5%, D50 is 75μm, and the specific surface area is 650m 2 / g; the mass percentage of hydrofluoric acid solution is 98.5%;

[0099] 2. In the atomization unit, the mixed system is atomized to obtain an atomization system; through the test of the aerosol tester, it can be known that the droplet particle size in the atomization system is 120 μm;

[0100] 3. At 0.3 MPa, in a heat shrink unit, the atomization system was heat-shrinked using nitrogen at a temperature of 300° C. for 10 min to obtain porous lithium fluoride.

[0101] Table 1

[0102]

[0103]

[0104]

[0105]

[0106] Test example

[0107] The porous lithium fluoride of Examples 1-32 and Comparative Examples 1-8 was subjected to BET test to obtain the specific surface area of ​​the porous lithium fluoride, as shown in Table 2.

[0108] The porous lithium fluoride of Examples 1-32 and Comparative Examples 1-8 was tested by a powder porosity tester to obtain the porosity of the porous lithium fluoride, as shown in Table 2.

[0109] The porous lithium fluoride of Examples 1-32 and Comparative Examples 1-8 was subjected to IC and ICP tests to obtain the purity of the porous lithium fluoride and the mass percentage of hydrogen fluoride, as shown in Table 2.

[0110] Table 2

[0111]

[0112]

[0113] As can be seen from Table 1 and Table 2, according to the comparison between Examples 1-3 and Comparative Example 1, when the Reynolds number of the mixed system is greater than 5000, lithium fluoride and hydrofluoric acid can be better mixed, and the prepared porous lithium fluoride has a higher specific surface area, porosity, and smaller D50, and at the same time, the purity is higher and the mass content of hydrogen fluoride is lower; according to the comparison between Examples 1, 4-8 and Comparative Examples 2 and 8, it can be seen that when the reaction temperature and reaction time of the heat treatment are within the specified range, lithium fluoride and hydrofluoric acid can be better mixed. The reaction is performed to generate lithium hydrogen fluoride, thereby increasing the specific surface area, porosity and purity of porous lithium fluoride, reducing the particle size and lowering the hydrogen fluoride content; According to Examples 1, 9-13 and Comparative Examples 3, 4 and 7, it can be seen that the droplet size of the atomized treatment needs to be moderate. If the droplet size is too small, the particle size of the porous lithium fluoride after drying is too small, resulting in the porous lithium fluoride being easily broken, the D50 being reduced, the specific surface area and the porosity being reduced, and vice versa, if the droplet size is too large, it is easy to agglomerate during drying, resulting in the D50 of the porous lithium fluoride being large, The purity is reduced and the hydrogen fluoride content is increased; According to Examples 1, 14-17 and Comparative Examples 5 and 6, when the pressure of the heat shrinkage treatment, the temperature of the inert gas and the treatment time are within the specified range, the lithium hydrogen fluoride can be fully decomposed and volume-shrunk to form a porous lithium fluoride with high specific surface area, high porosity and suitable D50, and hydrogen fluoride can be fully removed to improve the purity of the porous lithium fluoride and reduce the hydrogen fluoride content; According to the comparison of Examples 1-3, 18-21, 28-30, It is known that the premixing treatment can ensure the uniform mixing of lithium fluoride and hydrofluoric acid solution, which is beneficial to the preparation of porous lithium fluoride with high specific surface area, high porosity, low D50, high purity and low mass content of hydrogen fluoride; according to Examples 22-27, it can be known that the use of high-purity lithium fluoride and hydrofluoric acid is beneficial to the preparation of porous lithium fluoride with higher performance; according to the comparison of Examples 1, 31 and 32, it can be known that the ratio of lithium fluoride and hydrofluoric acid solution is beneficial to the preparation of porous lithium fluoride with higher performance within a certain range.

[0114] In summary, the preparation method of porous lithium fluoride provided by the present invention can prepare porous lithium fluoride with high specific surface area, high porosity, suitable particle size, high purity and low hydrogen fluoride content, and can realize continuous production of porous lithium fluoride, which is beneficial to improving the production efficiency of porous lithium fluoride.

[0115] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing porous lithium fluoride, characterized in that: The following steps are involved: 1) heat-treating the mixed system to obtain a reaction solution; wherein the mixed system comprises lithium fluoride and a hydrofluoric acid solution, and during the heat treatment, the Reynolds number of the mixed system is greater than 5000, the temperature is 30-60° C., and the time is 0.2-5 min; 2) atomizing the reaction liquid to obtain an atomization system, wherein the particle size of droplets formed in the atomization system is 30-200 μm; 3) Under a pressure of 0.1-0.5 MPa, the atomization system is subjected to a heat shrinkage treatment for 1-20 min using an inert gas at a temperature not lower than 200° C. to obtain the porous lithium fluoride.

2. The method for preparing porous lithium fluoride according to claim 1, characterized in that: The mixed system is prepared by a method comprising the following steps: The lithium fluoride and the hydrofluoric acid solution are pre-mixed for 1-3 minutes at a temperature of 20-40° C. and a pressure of 0.3-3 MPa to obtain the mixed system.

3. The method for preparing porous lithium fluoride according to claim 1 or 2, characterized in that: The purity of the lithium fluoride is 99-99.5%, the D50 is 20-100 μm, and the specific surface area is 200-700 m 2 / g.

4. The method for preparing porous lithium fluoride according to any one of claims 1 to 3, characterized in that: The mass percentage of the hydrofluoric acid solution is 95-99%.

5. The method for preparing porous lithium fluoride according to any one of claims 1 to 4, characterized in that: Step 3) also includes the following steps: The mixed gas obtained after the heat shrinkage treatment is condensed to obtain recovered hydrofluoric acid and recovered inert gas, and then the recovered hydrofluoric acid is returned to the pre-mixing treatment, and the recovered inert gas is returned to the heat shrinkage treatment.

6. A porous lithium fluoride, characterized in that: The specific surface area of ​​the porous lithium fluoride is 600-1400m 2 / g, porosity 30-80%; The D50 of the porous lithium fluoride is 20-100 μm.

7. The porous lithium fluoride according to claim 6, characterized in that: The purity of the porous lithium fluoride is 99-99.5%, and the mass percentage of hydrogen fluoride in the porous lithium fluoride is less than 500ppm.

8. A porous lithium fluoride device, characterized in that: It includes a heat treatment unit, an atomization unit and a heat shrinkage treatment unit; Wherein, the reaction liquid outlet of the heat treatment unit is connected to the inlet of the atomization unit; The atomizing unit is used for the atomizing treatment, and the heat shrinking treatment unit is used for the heat shrinking treatment.

9. The porous lithium fluoride device according to claim 8, characterized in that: The device further comprises a pre-mixing unit, wherein an outlet of the pre-mixing unit is in communication with an inlet of the heat treatment unit.

10. The porous lithium fluoride device according to claim 8 or 9, characterized in that: The device also includes a condensation unit, which is used for condensation treatment of the mixed gas, wherein the liquid phase outlet of the condensation unit is connected to the inlet of the premixing unit, and the gas phase outlet of the condensation unit is connected to the gas phase inlet of the heat shrinkage treatment unit.

11. A method for preparing lithium hexafluorophosphate, characterized in that: Lithium hexafluorophosphate is prepared by using the porous lithium fluoride described in claim 6 or 7 as a raw material.

12. An electrolyte, characterized in that: The electrolyte comprises lithium hexafluorophosphate prepared using the porous lithium fluoride according to claim 6 or 7 as a raw material.

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